Non-rigid atomic expressions
I gave a talk about the Canberra Plan on Tuesday (slides) in which I mentioned that I disagree with Lewis and Kim about the semantics of "pain": they say "pain" denotes whatever occupies the pain role in the species under consideration (or whatever is the relevant kind); I think "pain" rather denotes the property of being in a state that realises the pain role. One of the reasons I gave for my preference is that "pain" would be rather exceptional if it worked as Lewis and Kim believe.
What would be exceptional is that "pain" would not only be context-dependent but also index-dependent, i.e. non-rigid. Lewis explicitly says that "pain" is non-rigid in "Reduction of Mind", and I think this is required on his view to account for some of the things we say, like
1) it is possible that all animals in a world have pain, even though they do not all belong to a common species,
or
2) there are possible worlds where we have pain but are in a different brain state than we are when we actually have pain.
Here it seems that the reference of "pain" would have to vary between indices of evaluation.
There clearly are non-atomic expressions that behave like this: "the state that plays the pain role", "the closing mechanism", "the door", "my bike". These are all non-rigid and display both context-dependence and index-dependence. But I think this is entirely due to the occurrences of "the" and "my". I can't think of any atomic expressions in English (or German) that clearly behave like these complex expressions do.
(If there aren't any such expressions, 2D semantics in a sense leaves far too much freedom. When we learn a word, we learn its application conditions across counteractual situations; we never have to learn a full 2D matrix. The matrix automatically falls out of the diagonal.)
However, there are some unclear cases. Andy Egan mentioned "tall". It is certainly context-dependent. Is it also index-dependent?
3) If everybody were much taller than I, I wouldn't be tall.
That sounds okay. But it is easy to confuse index-variation with context-variation in such cases. (Compare "if 'leg' meant tail...".) Surely in the envisaged situation I would not be called tall, but I might still satisfy what is expressed by "tall" in the utterance context. As Weng Hong pointed out, it doesn't seem that I would suddenly become very tall just because everybody who is taller than me died (even though I might then come to be called tall). Moreover, this is certainly true:
4) it is possible that everybody be tall.
In a world where (4) is true, even the smallest person is tall. (I assume that some of the worlds that make (4) true have a smallest person.) Here the standards for "tall" do not appear to be set by the world of evaluation.
On the other hand, I don't know how to handle sentences like
5) if the sizes of the members of all species varied considerably, then every species would have members that are tall and others that are small,
which at least doesn't sound obviously false. Does it require index-variation or some semantic equivalent (such as assigning "tall" a hidden argument place for a pair of a contrast class and a world)?
Another worry (that Daniel Nolan brought up) is that if the behaviour of "tall" (and "funny" and "tasty" etc.) can be fully explained without index-dependence, then perhaps this explanation could be applied to the Lewis-Kim interpretation of "pain" as well.
What do you think? Are there good reasons to treat "tall" as index-dependent, or are there other candidates for atomic index-dependent expressions? And are there good tests for index-dependence that I'm missing?
Very interesting!
Just a side remark: I wasn't completely clear about the reason why you think that the non-rigidty claim is required on Lewis' view to account for things such as (1) and (2) above. Assume that expressions such as 'has pain' refer (wrt an index) to properties. Stipulate that 'has pain-1' non-rigidly refers wrt to the different indices to the different properties that play the pain-role in these indices (Ã la Lewis). Consider now the property that is had by something at an index iff the thing has the property 'has pain-1' non-rigidly refers to wrt that index. And stipulate that 'has pain-2' rigidly refers to that property. It seems to me that (1) and (2) would be as much true with 'have pain-1' in the place of 'have pain' as they would be with 'have pain-2' instead.